1. Field of the Invention
The present invention relates to a data receiving device and its associated method, especially to a data receiving device and its associated method of High Definition Multimedia Interface (HDMI).
2. Description of Related Art
HDMI is a common audio and video transmission interface. Please refer to FIG. 1, illustrating a conventional data receiving device 100 of an HDMI receiving end. The data receiving device 100 includes a phase detector (PD) 110, a phase interpolator (PI) 120, a phase lock loop (PLL) 130 and a digital loop filter 140. The original HDMI signal usually includes an HDMI data signal and an HDMI clock. The HDMI data signal may include color information of images. After being properly processed, the HDMI clock can be used for sampling the HDMI data signal to recover the color information. As shown in FIG. 1, the PLL 130 generates a reference clock CK_PLL by referring to the HDMI clock. The reference clock CK_PLL is in phase with the HDMI clock but its frequency is a multiple of the frequency of the HDMI clock. The PI 120 adjusts the phase of the reference clock CK_PLL and outputs a data recovery clock CK_RCV to the PD 110. The PD 110 compares the phases of the HDMI data signal and the data recovery clock CK_RCV and outputs a phase detection signal that indicates a phase relation between these two signals, according to which the PI 120 adjusts the phase of the reference clock CK_PLL. Practically, the data recovery clock CK_RCV may probably be unstable if the phase detection signal changes rapidly during the phase adjustment of the PI 120, and to prevent this situation from happening, the digital loop filter 140 is usually used to make the phase detection signal a relatively stable signal in time by filtering out its high frequency part.
The HDMI transmission modes includes HDMI 1.4 and HDMI 2.0, which are widely used or will be common soon. According to the HDMI 1.4 specification, the data rate of the HDMI data signal ranges from 250 Mbps to 3.4 Gbps and its corresponding HDMI clock ranges from 25 MHz to 340 MHz; on the other hand, according to the HDMI 2.0 specification, the data rate of the HDMI data signal ranges from 3.4 Gbps to 6 Gbps and its corresponding HDMI clock ranges from 85 MHz to 150 MHz. Please refer to FIG. 1. When the data receiving device 100 is applied to equipment supporting only HDMI 1.4, the PLL 130 can always use a frequency multiple of 10 to make the frequency of the reference clock CK_PLL be 10 times the frequency of the HDMI clock, which is identical to the frequency of the HDMI data signal. Therefore, the data recovery clock CK_RCV, which is generated by properly adjusting the phase of the reference clock CK_PLL, can be used to sample the HDMI data signal to recovery the data carried by the HDMI data signal. Similarly, when the data receiving device 100 is applied to equipment supporting only HDMI 2.0, the PLL 130 uses a frequency multiple of 40 to make the frequency of the reference clock CK_PLL be 40 times the frequency of the HDMI clock, which is identical to the frequency of the HDMI data signal, so as to sample the HDMI data signal. Considering a case that the data receiving device 100 is applied to equipment supporting HDMI 1.4 and HDMI 2.0 at the same time, if the frequency multiple of the PLL 130 is determined by detecting the frequency of the HDMI clock, for example, if the HDMI clock is detected to be in the range of 25 MHz˜85 MHz or 150 MHz˜340 MHz, the data receiving device 100 finds that the transmission mode in use is HDMI 1.4 and determines the frequency multiple to be 10; if, however, the frequency of the HDMI clock is detected to be in the range of 85 MHz˜150 MHz, the data receiving device 100 cannot determine the transmission mode of the HDMI data signal.
Another applicable method is to utilize the display data channel (DDC) to transmit the HDMI mode in use so that the HDMI receiving end can determine the HDMI mode when receiving the HDMI data signal. If, however, the transmission of this information is not agreed in advance between the transmission end and the receiving end or interferences which cause data loss occur during the information transmission, the data receiving device 100 cannot operate properly and therefore the audio and video contents cannot be presented normally.